Just to clarify about what most folks call crabapples. Like most people I grew up calling any wild tree with smaller apples crabapples, which actually is far from the truth for the most part. Real crabapples are actually those heavy flowering trees we see in late spring in peoples yards. For the most part they are grown for looks or as a pollinator for domestic type apple trees. The majority of them produce small apples around 1/2" or even less. Now the one exception is a variety called Dolgo, which has slightly oval apples 1 1/2" to almost 2". Those are the real red ones you see in late summer and the ones I use to make crabapple jelly, which has a bright red colour to it. Even the insides are red. Most real crabs including Dolgo are quite sour and not good deer fodder.
So most trees in old orchards or along fence lines that we see are actually old domestic type trees that have gone wild and with no maintenance they will produce small apples mostly, hence why folks tend to call them crabs. The best way to find out if deer might like them is to actually taste them to see how bitter they are. If they're not too bad then the deer should like them, if they're real sour/bitter like those ones that stay yellow all season the deer don't seem to touch them at all.
Here's what the Dolgo look like. A 1/2 hour of picking this year netted us 20 jars of jelly this year. So good.
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Cheers